The objective of this project is to elucidate the natural history and pathophysiology of airflow obstructive disease (AOD) by determining from longitudinal analysis of lung function data obtained in the population enrolled in the Tucson epidemiologic study of AOD (P-1) the normal patterns of change and the altered patterns of change which lead ultimately to frank abnormality together with the factors which induces such altered change. Observations concerning the normal changes in CO diffusing capacity and the effects of smoking and smoking cessation on this measurement will be extended to include analysis of longitudinal data currently being collected in Survey 12. Structure - function relationships will be assessed as the site and nature of changes resulting in AOD will be elucidated by detailed physiological assessment and by employing new objective methods of analyzing data obtained on CT scans. The expiratory CT scan will be further explored as a noninvasive means of assessing lung morphology. The sensitivity of the expiratory CT scan will be assessed, including the effects of age, normal limits, the ability to detect early emphysema, the effect of asthma and age of onset of asthma. Phenomena which contribute to preservation or deterioration of lung function with aging in the absence of overt disease will be examined using physiologic and radiological techniques.